This invention generally relates to an energy management system subjected to extremely high impacts loads applied thereto, and more particularly, to a railcar draft gear housing configured to offer enhanced energy dampening capabilities to a railcar draft gear assembly while advantageously being both stronger and weighing significantly less than the same type prior art draft gear housing.
Energy management systems are used in a variety of industrial applications wherein a vehicle is subjected to extremely high impact loads and forces during operation. For example, in the railroad industry, an energy management system in the form of draft gear assemblies have been in widespread use on rolling stock for many decades. A railcar draft gear assembly is used to cushion shocks and dissipate energy encountered by railway rolling stock during make-up and/or operation of a train consist on track structure. The draft gear assembly typically nests in a pocket of a railcar center sill. A typical draft gear assembly includes a housing having a closed end, which abuts a rear wall of the pocket within the car sill, and an open end.
It is recognized by persons skilled in the railcar draft gear art, these draft gear assemblies must maintain certain minimum shock absorbing capacity during in-track service. The railcar industry furthermore continues to express interest in new, higher capacity draft gear assemblies. Presently, minimum shock absorbing capacity is specified by the Association of American Railroads (AAR) Standards.
To accomplish and meet these standards, it is known to equip such railcar draft gear assemblies with a suitable spring biased mechanism arranged primarily within the confines of the draft gear housing. A portion of the spring biased mechanism extends axially beyond the housing to engage and operate in combination with a follower plate. During in-track service, it is inevitable that energy imparted to the railcar draft gear exceeds the reaction capacity of the spring biased mechanism. As such, the draft gear spring biased mechanism assumes an xe2x80x9cover-solidxe2x80x9d condition and all remaining energy is imparted to the draft gear housing. As will be appreciated by those skilled in the art, and while occurring on a frequent basis, the energy required for the spring biased mechanism to assume an xe2x80x9cover-solidxe2x80x9d condition is exceedingly substantial, i.e. in excess of 600,000 inch pounds. After the spring biased mechanism reaches its xe2x80x9cover-solidxe2x80x9d condition, any excessive energy is thereafter transferred through the draft gear housing into the car sill and car body and, ultimately, to the lading carried therewithin. Such energy imparted to the car frequently causes significant damage to the lading carried within the railcar.
The railcar draft gear housing has been heretofore designed from exceedingly massive ferrous metal, i.e., steel castings which can withstand repetitive high energy impacts after the spring biased mechanism has achieved an xe2x80x9cover-solidxe2x80x9d condition without stress break or fracture. Such castings, however, typically require further machining and/or other secondary operations prior to incorporation of the spring biased mechanism therewithin. As will be appreciated, such processes and/or operations require trained manual efforts adding to the draft gear assembly costs without contributing any appreciable benefit to its performance characteristics.
With ever increasing fuel costs, there are continuing and concerned efforts in the railroad industry to increase productivity. Historically, increases have been achieved by increasing the rolling stock comprising a train consist and additionally the capacity of the railcars. Of course, increasing the rolling stock comprising a train consist furthermore adds to the dynamic energy transferred between adjacent cars comprising the consist. AAR Standards regarding regulating the size of the railcars along with the practical load limit of today""s railroad track system, however, has generally been reached. Accordingly, attention is now being directed to other areas. For example, lightening of the overall weight of the rolling stock without sacrificing or unreasonably increasing costs is an on-going goal and would improve railcars.
In the mid 1990""s, the North American railroad industry transported approximately 1.2 trillion ton-miles of lading in a fleet consisting of about 1.5 million railroad cars with a revenue of about $31 billion. Since the mid 1990""s, such statistics have only increased. Accordingly, and although minor improvements may seem trivial when viewed with a narrow perspective, the overall benefits to be achieved can be significant. Even when considering individual train consists, it will be apparent, in a train consist comprised of 100 cars, a mere five pound reduction in weight of duplicated railcar components translates to one-half ton weight reduction per train. As will, be appreciated, reducing the cumulative empty weight of the 100 car train consist by one-half ton allows that same train consist to transport an additional 1000 pounds of lading with no additional costs being added.
Thus, there is a need and continuing desire for a railcar draft housing which is even stronger than known draft gear housing of the same type and allow such draft gear housing to sustain excessive energy applied thereto but is also significantly less weight whereby contributing to fuel savings and increased train lading capacity and which can be manufactured to such close tolerances whereby substantially eliminating the need for subsequent and expensive machining and/or other secondary operations prior to actual use on the railcar.
In view of the above, and in accordance with the present invention, there is provided a new and improved housing for an apparatus or energy management system. In one form, there is provided a railroad draft gear housing having improved operating characteristics which can be manufactured at a lower cost than heretofore known draft gear housing of a similar type. Although the material of the railcar draft gear housing has been modified along with its cross-sectional dimensions, it advantageously remains and retains its interchangeability with draft gear housings serving the same purpose while offering an improved strength to weight ratio. The present railcar draft gear housing is especially advantageous in that it is not only stronger than prior railcar draft gear housings of the same type, it is also significantly lighter in weight thereby contributing to fuel savings and/or increased lading capacity for the associated railcar.
In accordance with a first aspect, there is provided a railcar draft gear housing which combines the strength, ductility, fracture toughness and wear resistence of steel with the castability and product economies of ductile iron. The draft gear housing of the present invention is produced from an austempered ductile iron casting having an open end, a closed end, and wall structure axially extending between the housing""s ends. The wall structure of the housing defines an axial section between and spaced from the ends. In accordance with the present invention, the axial section of the wall structure is designed and configured to act as an elastic member which is capable of withstanding impact energy imparted to the casting in excess of 81,000 inch pounds while retaining and exhibiting substantially linear elasticity wherein the resultant ratio of stress to energy input remains substantially constant. That is, and unlike heretofore known steel draft gear housings, the wall structure of the draft gear housing is designed and configured to flexibly distort within a yield range of austempered ductile iron whereby advantageously serving to absorb, dissipate and return energy imparted thereto during operation of the railcar and thereby enhancing overall operation of a draft gear assembly, of which the housing forms an integral part, without increasing the cost of such assembly.
Research has revealed superior results are obtainable when the railcar draft gear housing is preferably formed from a grade of ductile iron selected from the group consisting of: ASTM Grade 1 ductile iron through ASTM Grade 5 ductile iron. To accomplish the preferred goal of interchangeability mentioned above, the railcar draft gear casting preferably measures between about 14 inches and about 29 inches in axial length between the open and closed ends. Moreover, and to significantly lessen the overall weight of the draft gear assembly, the axial section of the sidewall structure for the railcar draft gear housing has a cross-sectional area measuring between about 9.5 inches and about 17.5 inches. Accordingly, the casting for the draft gear housing advantageously weighs only generally between about 75 lbs. and about 150 lbs.
In accordance with another aspect, there is provided a railcar draft gear housing produced from an as cast austempered ductile iron casting having an open end, a closed end, and wall structure axially extending between the ends. The wall structure defines an axial section spaced from and between said ends for absorbing, dissipating and returning energy imparted to said housing resulting from impact loads applied thereto. Additionally, the axial section of the wall structure has a minimum yield strength ranging between about 100 ksi. and about 150 ksi., with a minimum compression in 2 inches ranging between generally about 3% and about 15%, and with a BHN within a range of generally between about 300 and about 500. The ability of the axial section of the housing""s wall structure to absorb impacts without fracture or breakage beyond a range permitted with steel castings of the prior art coupled with the ability of the as-cast austempered ductile iron casting to return to its original state or condition provides the draft gear housing with a unique ability and structural characteristic contributing significantly improved performance to the draft gear assembly during railcar operation without requiring costly and time-consuming machining and other secondary operations to be performed on the draft gear housing.
The railcar draft gear housing casting is furthermore preferably configured with a series of openings arranged toward the housing""s closed end to eliminate and minimize unnecessary mass and reducing the overall weight thereof, thus, increasing the load carrying capacity of the railcar. In a preferred embodiment, the sidewall structure of the casting, including the axial section, has a generally cylindrical cross-sectional configuration extending between the housing""s ends. The axial section of the wall structure has a cross-sectional area measuring only between about 9.5 inches and about 17.5 inches. Preferably, the generally cylindrical cross-sectional configuration of the casting, at least through the axial section, has a generally uniform thickness whereby allowing the railcar draft gear housing to retain and exhibit substantially linear elasticity wherein the resultant ratio of stress to energy input remains substantially constant even after the energy imparted solely to the housing exceeds 81,000 inch pounds.
Still another aspect relates to providing a railcar draft gear assembly including a spring assembly for dissipating energy forces imparted to said draft gear assembly and a housing which surrounds the spring assembly. The draft gear housing is formed from a high strength, low-alloy, austempered composite metal material whose mechanical properties can be varied over a wide range by a suitable choice of heat treatment and having a density of generally about 0.25 lb./cu. in. The housing includes an open end, a closed end, and wall structure axially extending between the opposed ends. The housing wall structure includes a tubular axial section designed to offer over-solid energy absorption protection to the draft gear assembly. That is, and following the spring assembly acting to effect energy absorption equal to or in excess of 600,000 inch pounds and being compressed into an xe2x80x9cover-solidxe2x80x9d condition, the draft gear housing is designed and configured to provide the draft gear assembly with an at least an additional 81,000 inch pounds of energy absorption capability while retaining and exhibiting substantially linear elasticity wherein the resultant ratio of stress to energy remains substantially constant whereby enhancing the overall life expectancy of the railroad equipment.
According to still another aspect, there is provided an apparatus which, during operation, is subjected to repeated axial loadings applied thereto. The apparatus includes an as-cast elongated member formed from an austempered composite material having a density of about 0.25 lb./cu.in., and wherein said elongated member has first and second axially spaced ends with wall structure axially extending between said ends, with said wall structure including an axial section configured and designed to offer over-solid energy absorption protection for said apparatus and is configured to withstand impact energy in excess of 81,000 inch pounds while retaining and exhibiting substantially linear elasticity wherein the resultant ratio of energy input remains substantially constant.
Accordingly, one object of the present invention is to provide a new and improved housing for an apparatus or energy management system which is not only interchangeable with but is also stronger and lighter than a comparable energy management system steel housing now in use whereby contributing to fuel savings and/or increased lading capacity for the apparatus or vehicle with which the energy management system is in operable combination.
Another object of the present invention is to provide a railcar draft gear housing having at least one axial section capable of absorbing, dissipating and returning impact forces imparted to the housing whereby adding enhanced dampening of excessive energy imparted thereto and, thus, contributing to improved performance of a draft gear assembly than heretofore obtainable with known steel housings.
Yet another feature of the present invention relates to the provision of a railcar draft gear housing which is made of a stronger base material which permits openings to be designed into the housing to enhance weight and material reduction essentially without sacrificing strength.
An even further object of this invention relates to the provision of a railcar draft gear housing which is made from a high strength, low alloy, austempered composite material which is lighter in weight and less costly than materials heretofore used for railcar draft gear housings.
These and other objects aims and advantages of the present invention will become readily apparent from the following detailed description, drawings and appended claims.